Metallurgical process



March 5, 1968 J. F. WALLACE ETAL METALLURGI CAL PROCES S 2 Sheets-Sheet 1 Filed Nov. 17, 1964 Inventors John F. Wallace Robert W. Newyear March 5, 1968 J. F. WALLACE ETAL I METALLURGICAL PROCESS 2 Sheets-Sheet 2 Filed Nov. 1'7, 1964 Inventors John F. Wallace 8 Robert W. Newyeur aid W States Patent Ofilice p asrznzs Patented Mar. 5, 1968 3,372,025 METALLURGTCAL PRGCESS John F. Waliace, Shaker Heights, Ohio, and Robert W. Newyear, Latrobe, Pa, assignors to Vulcan Mold and Iron Company, Latrobe, Pa., a corporation of Fenusylvania Filed Nov. 17, 1964, cr. No. 411,780 3 Qlaims. (Cl. 75-123) ABSTRAUT F THE DISCLOSURE A method of altering the composition and microstructure of cupola melted gray iron by introducing anthracite coal. The anthracite coal increases the length of the graphite flakes. The pearlite in the matrix is reduced, the eutectic cell count of the structure is reduced, and the amount of ferrite in the matrix of the iron is increased.

This invention relates to a process of making a new and improved iron used in casting ingot molds and stools. More particularly the invention relates to the injection of anthracite coal into cupola melted gray iron by a stream of air or other inert gases below the surface of the molten cupola iron.

Most cast iron ingot molds fail primarily because of the thermal stress, erosion and oxidation. Thermal stress occurs when the molten steel is poured into a mold caus ing a large temperature differential within the mold wall. To solve this problem, iron which has the ability to yield at low stresses and has the ability to reduce the stresses to a low level by yielding under the action of these stresses, is preferred. Such iron must necessarily have a very low tensile strength in the range of 5,000 p.s.i. to 14,000 p.s.i. Blast furnace iron meets this requirement. Blast furnace iron in the molten state has a small number of nuclei for graphitic solidification and consequently upon solidification has a low eutectic cell count. The carbon in the blast furnace iron forms very large, long and thick graphite flakes in a matrix which is predominantly pearlite and with a small amount of ferrite.

Cupola melted iron has a large number of nuclei for graphitic solidification and consequently upon solidification has a high eutectic cell count. The carbon in cupola melted iron forms small, short and thin graphite flakes in a matrix that is predominantly pearlite. This structure has more strength than the blast furnace iron structure and it is generally preferred because the normal applications of gray iron castings require considerable strength. This iron has less ability to yield under thermal stress and resists the action of the stresses as contrasted to iron which yields under these stresses.

The ideal iron for molds and stools should have a low tensile strength. Such iron would have a structure consisting of very long and large graphite flakes in a soft, low strength matrix consisting primarily of ferrite.

The present invention produces a low tensile strength iron from cupola melted gray iron which is better than blast furance iron because it has less pearlite in the matrix than blast furnace iron. This is done by injecting anthracite coal below the surface of molten cupola gray iron be it either in a ladle, holding ladle, mixing ladle, holding furance, or other vessel or through the cupola tuyeres.

Increasing the graphite of iron by injection of carbonaceous materials is old. Injection of most, if not all, carbonaceous materials reduces the length of the graphite flakes and makes the iron undesirable for the specific purpose of large mold manufacture. Anthracite coal is the only known material which, when injected into cupola melted gray iron, produces an increase in length of graphite flakes by apparently reducing the nuclei and eutectic cell count and at the same time reduces the amount of pearlite and increases the amount of ferrite, thereby providing a desirable low strength matrix and graphite structure. Therefore, by using anthracite coal, cupola melted gray iron may be used instead of blast furnace iron in the manufacture of large ingot molds and stools.

We provide a method of alternating the composition and microstructure of cupola melted gray iron which comprises introducing anthracite coal to the cupola melted melted gray iron. We increase the size of the graphite flakes so that they resemble graphite flakes in the microstructure of the optimum blast furnace iron. We reduce the amount of pearlite in the matrix of the cupola melted gray iron by introducing anthracite coal. We preferably increase the size of the graphite flakes of the cupola melted gray iron and at the same time reduce the amount of pearlite in the matrix of the iron by introducing anthracite coal below the surface of the cupola melted gray iron. We provide that the anthracite coal injected into cupola melted gray iron has a fineness in the range of 4 to 2-00 mesh. We provide that an amount of anthracite coal is injected to raise the normal base cupola iron a minimum of 0.2% carbon by weight. We preferably in-' ject the anthracite coal by a stream of gas consisting of either inert gas or air. We provide a low tensile strength cupola gray iron containing a low eutectic cell count and large thick graphite flakes in a matrix which is predominantly ferritic by treating the cupola melted gray iron with anthracite coal below the surface of the molten metal. The composition comprises 0.75% to 2.50% silicon, 0.01% to 1.50% sulphur, 0.01% to 0.450% phosphorous, 0.40% to 1.20%. manganese, 3.00% to 4.70% carbon, and the balance of iron with usual impurities in the normal amounts.

We preferably provide a cupola melted gray iron having a tensile strength between 5,000 p.s.i. to 14,000 p.s.i.

Other details, objects and advantages of this invention will become apparent as a following description of a present preferred embodiment and a present preferred method of practicing the same proceeds in which FIGURE 1 is a photomicrograph taken at power of unetched typical blast furnace iron;

FIGURE 2 is a photomicrograph taken at 100 power of typical blast furnace iron etch by 2% picral and 2% HCl;

FIGURE 3 is a photomicrograph taken at 100 power of unetched cupola melted iron;

FIGURE 4 is a photomichograph taken at 100 power of nital etched cupola melted iron;

FIGURE 5 is a photomicrograph taken at 100 power of unetched cupola melted iron treated with anthracite coal; and

FIGURE 6 is a photomicrograph taken at 100 power'of nital etched cupola melted iron treated with anthracite coal.

FIGURE 1 shows a photomicrograph taken at 100 power showing typical optimum unetched blast furnace iron.

FIGURE 2 shows a photomicrograph taken at 100 power showing typical optimum blast furnace iron etched with 2% picral and 2% Hill. Long, large graphite flakes 10 are in a matrix having ferrite 12 shown as white adjacent to the flakes 10. Adjacent to the ferrite 12 are areas of pearlite 14. This blast furnace iron is low in nuclei and low in eutectic cell count and has very large, long, thick graphite flakes 10 in a matrix which comprises ferrite 12 and pearlite 14 but which is predominantly pearlite 14. It has a tensile strength range from 5,000 p.s.i. to 15,000 p.s.i. The typical composition of blast furnace iron used for the production of ingot molds and stools is as follows 1.50% silicon, 0.035% sulphur, 0.15% phosphorous, 0.75% manganese, 4.20% carbon. The long extended graphite flakes 10 are preferred because graphite weakens the structure because it has little strength compared to iron. Therefore, any applied stress on the iron must be borne by the matrix structure comprising pearlite 14, and ferrite 12. The ferrite 12 in the matrix provides less resistance to flow within its confines. Pearlite 14 is a harder substance and provides considerable resistance within its confines.

FIGURE 3 is a photomicrograph taken at 100 power of typical unetched cupola melted iron.

FIGURE 4 is a photomicrogr'aph taken at 100 power of typical melted cupola iron which has been etched with nital. Short, thin graphite flakes 16 are set in a matrix comprising predominantly pearlite 18, which is a hard substance. This iron is referred to as one that is unsaturated with carbon. It contains considerable nuclei for graphitic solidification and upon solidification it produces an iron that has a high eutectic cell count, forming short, thin flakes 16 in a matrix that is predominant pearlite 18. The white portions are shown as ferrite 17. This structure customarily results from the compositions of material melted and the melting conditions in the cupola and has more strength than blast furnace iron. This structure is generally preferred by most users because the normal applications of gray iron castings require considerable strength. A typical composition for this cupola melted gray iron shown is as follows, 1. 60% silicon, 0.100% sulphur, 0.12% phosphorous, 0.60% manganese and 3.50% carbon.

FIGURE shows a photomicrograph taken .at 100 power of a typical cupola melted iron which was treated with anthracite co'al.

FIGURE 6 shows a photomicro-graph taken at 100 power of a typical cupola melted iron which was treated with anthracite coal and etched with nital. This structure contains long, thick graphite flakes 20 'and a matrix comprising ferrite 22 shown in white adjacent to the flakes 20 and pearlite 24 is shown in gray.

This ferritic structure is contrasted to a pearlitic structure of blast furnace iron and cupola iron, untreated with anthracite co'al that contains platelets of combined carbon, carbide. Graphite flakes 20 have little strength compared to iron and stress applied to the iron must be borne by the matrix structure, and the greater the length and thickness of these graphite flakes 20, the larger the concentration of stress on the matrix and 'at the edges of the flakes 20. Therefore, the ferritic matrix provides the least resistance to flow within its confines because no hard particles are present to interfere with such flow or yielding. This matrix has more ferrite than the blast furnace matrix, and, therefore, is preferable to this extent over blast furnace iron. Cupola melted iron that normally solidifies to provide the structures shown in FIGURES 3 and 4 was treated in the molten condition by injecting anthracite coal below the molten iron surface to produce the iron shown in FIGURES 5 and 6.

The anthracite coal can be injected in the cupola, in a mixing ladle, in a holding ladle, in a holding furnace r other VCS QI- Generally, powdered anthracite coal of a fineness from 4 to 200 mesh size is injected by a stream of air or nitrogen or other inert gases. The introduction of this anthracite coal increases the carbon content of the iron by dissolving in the iron and increases the amount of graphite in the iron after solidification. The anthracite coal at the same time influences the structure of the iron differently than any other carbonaceous material injected into molten iron. Most carbonaceous materials increase the carbon content of the molten iron and these carbonaceous materials at the same time increase the nuclei for graphite solidification Whereas anthracite coal decreases the nuclei for graphite solidification and increases the length of the graphite flakes, decreases the amount of pearlite and increases the amount of ferrite in the matrix of the iron. The anthracite coal is normally injected in a cupola through cupola tuyeres under an air pressure between 40 and 150 p.s.i. If the cupola melted gray iron is in a ladle, normally a lance extending to the bottom of the ladle has anthracite coal forced through it by air, nitrogen or other inert gases under 40 to 150' pounds of pressure and as the anthracite coal rises to the top, the carbon from the anthracite coal is dissolved in the cupola melted gray iron, producing longer flakes and at the same time increasing the amount of ferrite in the matrix.

Depending on the carbon content desired, at a minimum temperature of 2600 F., between 6 and 30 pounds of anthracite coal are added per ton of cupola melted gray iron to produce the desired result shown in FIG- URES 5 and 6.

Example 1 Cupola melted gray iron at a temperature range between 2600 and 2900 F. had powdered anthracite coal injected through the cupola tuyeres and produced 1.0% to 1.80% silicon, 0.050% maximum sulphur, 0.15% maximum phosphorous, 0.80% maximum manganese and between 4.00% to 4.30% carbon, and the balance of iron h'ad usual impurities in the normal amounts.

Example 2 Cupola melted gray iron had powdered anthracite coal between 4 and 200 mesh injected through the cupola tuyeres at a temperature range between 2600 F. and 2900" F. producing an iron having a eutectic cell count and cells per square inch in a matrix which was 90% ferritic and only 10% pearlitic, the pearlite being medium fine, the material having 1.64% silicon, 0.052% sulphur, 0.110% phosphorous, 0.68% manganese, 4.15% carbon, and 0.02% chromium and the balance of iron with the usual impurities in normal amounts.

Example 3 Cupola melted gray iron was injected with powdered anthracite coal through the cupola tuyeres at a temperature range between 2600 F. and 2900" F. producing an iron having a eutectic cell count between 100 and '1 10 cells per square inch in a matrix which was 90% ferritic and 10% pearlitic, the pearlite classified as medium fine, the material comprising 1.58% silicon, 0.064% sulphur, 0.100% phosphorous, 0.72% manganese, 4.10% carbon and no chromium and the balance of iron with usual impurities in normal amounts.

While we have shown and described a present preferred embodiment and have illustrated a present preferred method of practicing the same, it is to be distinctly understood that the invention is not limited thereto but may be variously embodied and practiced within the scope of the following claims.

We claim:

1. A method of increasing the size of the graphite flakes of cupola melted gray iron and reducing the amount of pearlite in the matrix of the iron for use in making ingot molds and stools which comprises introducing sufiicient powdered anthracite coal below the surface of the molten cupola gray iron to raise the normal base cupola iron a minimum of 0.20% carbon by weight, the powdered S) anthracite coal having a fineness in the range between 4 to 200 mesh.

2. A method of increasing the size of the graphite flakes of cupola melted gray iron and reducing the amount of pearlite in the matrix of the iron for use in making ingot molds and stools which comprises introducing sufficient powdered anthracite coal below the surface of the molten cupola gray iron by a stream of gas selected from the group consisting of air and inert gas to raise the normal base cupola iron 21 minimum of 0.20% carbon by weight, the powdered anthracite coal having a fineness in the range between 4 to 200 mesh.

3. A low tensile strength cupola melted gray iron produced by the process of claim 1 comprising 0.75% to 2.50% silicon, 0.010% to 0.150% maximum sulphur, 15

0.01% to 0.450% phosphorous, 0.40% to 1.20% manganese, 3% to 4.70% carbon, and the balance of iron With usual impurities in normal amounts and characterized by a low eutectic cell count and by large thick graphite flakes in a matrix which is predominantly ferritic.

References Cited UNITED STATES PATENTS 584,781 6/1897 Howe 75-130 FOREIGN PATENTS 2,889 1870 Great Britain. 587,480 4/ 194 7 Great Britain.

CHARLES N. LOVELL, Primary Examiner.

DAVID L. RECK, Examiner.

P. WEINSTEIN, Assistant Examiner. 

